This application is based on Japanese Patent Application No. 2004-324228, filed Nov. 8, 2004, corresponding to Japanese Patent Publication No. 2005-168284, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a spiral support to be used in bundling various cables including wires, specifically optical fiber cables such as aerial optical fiber cables or the like into one bundle unit. In addition, the present invention relates to the installation method of the same and the cable laying method using the spiral support.
2. Description of the Related Art
Such a spiral support is composed of one-way spiral formed from one end to the other and is categorized into 2 groups in terms of its length, which makes the cable laying method different.
One is a tightly wound spiral support that is constricted along its axis direction and has a total length that can cover a predetermined span corresponding to the distance between support posts such as electric poles after the spiral support is pulled to be laid out. This type of the spiral support is installed in such a way that the spiral support is fitted on a support wire (messenger wire) so as to house the messenger wire thereinside and then pulled along the messenger wire. In this case, one end of the spiral support is attached on one support post and then the other end is attached on the other support post after having been pulled (See, Examined Patent Application Publication No. S52-4033).
The other one is a short, relatively-rigid spiral support that has a total length of for example 1.5 m, which is much shorter than the predetermined span, and has a male and female connector (or joint) respectively on both ends. This spiral support is installed in such a way that one end of the spiral support is fitted on the messenger wire that has been stretched in advance; the spiral support is rotated in the spiral direction so as to allow the messenger wire to be housed inside the spiral support; another spiral support of the same type is connected to the other end of the previous spiral support; and then these procedures will be repeated until the sufficient number of the spiral supports that can cover the predetermined span is installed. Then, both ends of the connected spiral supports are attached to the messenger wire near each support post to complete the installation (See, Japanese Patent Application Laid-open Publication No. 2002-345116).
However, regarding such related-art spiral supports, either when the singular spiral support that can cover the predetermined span is installed (the former one) or when plural short spiral supports are installed by connecting or jointing them (the latter one), there has been the following disadvantage.
Since the former one is like a long coil, when such a spiral support is installed on the messenger wire that has been stretched in advance, the one end thereof is fitted on the messenger wire, and then the spiral support has to be continuously rotated in the spiral direction so as to allow the messenger wire to be housed inside until all the length thereof is installed.
Such installation is laborious, especially, when the diameter of a wire constituting the spiral support is larger. In addition, when the number of rotations is increased, such installation imposes a huge burden on a worker.
Moreover, when the spiral support is pulled to cover the span between the two support posts after it has been installed on the messenger wire, it is helpful that the rear end (opposite to the end to be pulled) is attached to the support post. However, when the spiral support is pulled along the messenger including a branch wire to form a T-shape therein, the spiral support has to be rotated to pass through the branch wire, which makes it impossible that the rear end is attached on the support post.
Nevertheless, if the rear end is not prevented from leaving the support post, the spiral support cannot be pulled. Therefore, when there is such a T-branch in the messenger wire, it is very difficult to install the spiral support of this type.
The latter one is more practical than the former one, when the spiral the messenger wire that has been stretched in advance includes T-branches.
However, a plural of short spiral supports have to be connected by connecting a female connector of one spiral support to a corresponding male connector of another, which costs labor and time. In addition, every time the short spiral supports are connected, the number of the connectors is increased accordingly. The connectors are positioned at random along the spiral direction, which may hinder the movement of the spiral supports when the spiral supports are pulled along the messenger wire., In a worst case, when some connectors are caught up somewhere in the messenger wire, the spiral supports cannot be pulled any more, resulting in a halt in installation.
In addition, when there is a branch for example in a T-shape somewhere in the messenger wire, it is difficult that the short spiral supports are rotated in one direction in order to pass through the branch. This is because the connector is more rigid than any other portion of the spiral supports and thus the spiral support lacks flexibility as a whole. Therefore, it is difficult to install such a spiral support when the messenger wire includes T-branches.
Therefore, when such spiral supports are installed on the messenger wire including a T-branch, installation has to be halted in front of the T-branch and then started over for the rest of the messenger wire after the T-branch, which is rather troublesome.
The present invention has been made in order to eliminate the above disadvantages and an aspect thereof is a provision of a spiral support that facilitates installation without requiring connection means such as connectors or the like, an installation method of the spiral support, and a cable laying method using the spiral support.